In a semiconductor integrated circuit, a silicon nitride film (SiN film) is used for a wide range of applications including an etching stopper, a sidewall spacer, and a stress liner for generating a distortion in a channel region, in addition to an insulating film. In a case of forming a thin film in a semiconductor manufacturing process, in addition to satisfactorily embedding fine patterns and good film quality, it is necessary to lower the temperature of a film forming process according to demands for suppression of migration of wirings, solidification of semiconductor devices and so forth.
However, for example, a nitriding gas such as an ammonia gas or the like is hardly nitrided unless it is subjected to a high temperature treatment. A silicon nitride film may be formed at a relatively low temperature by activating the nitriding gas with plasma. However, when the silicon nitride film is formed by plasma film formation, there is a problem that a substrate is damaged by energy used to turn a gas into plasma.
Conventionally, there is known a technique for forming a film by activating a process gas supplied onto a substrate placed in a processing container while irradiating an interior of the processing container with an ultraviolet ray. However, this technique has a problem that the bond of an already deposited silicon nitride film is broken when the substrate is irradiated with the ultraviolet ray. In addition, when the interior of the processing container is irradiated with the ultraviolet ray through a transmission window installed in the processing container, a silicon nitride film may be formed on a surface of the transmission window exposed in the processing container, which may inhibit the ultraviolet ray from being irradiated in the interior of the processing container.